When resecting a floor-of-mouth (FOM) squamous cell carcinoma that abuts a nonirradiated mandible, if neither clinical examination nor preoperative studies have shown evidence of bony tumor invasion and if the periosteum is histologically positive for cancer on frozen section and the underlying bone is grossly normal, a segmental resection of the mandible is required. A marginal resection is never appropriate.

Historically, when an FOM tumor abutted the mandible, a complete segment of mandibular bone was resected en bloc with the tumor.1 It was believed that the FOM lymphatics drained through the mandibular periosteum and bone to the neck, so that en bloc resection decreased the risk of later neck disease. Unfortunately, the segmental mandibulectomy left the patient with a significant functional and aesthetic deficit. Once Marchetta et al2 and Carter et al3 demonstrated that cancer spreads to the mandible by direct invasion rather than lymphatic spread, preservation or partial resection of the mandible became oncologically feasible. The question became how to select appropriate patients with oral cancer for segmental or partial-thickness (marginal) mandibular resection.